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First 2 pics look like dust, mold only grows on moist surfaces, 3rd pic maybe, 4th pic possibly. The only way to know for sure is to take a sample and have it tested. There are inexpensive test kits available, here's a link to one.https://www.amazon.com/Mold-Armor-FG500-Yourself-Test/dp/B002MPPYVQ/ref=sr_1_6?ie=UTF8&qid=1475684372&sr=8-6&keywords=mold+test+kit
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I said the PVC pipe looked the most like mold. If you want to be sure you have to have it tested. The test results if positive will also tell you what the potential issues are with that type of mold.